Zel by Amanda Meuwissen

An assassin in disguise is not meant to fall for their target… but Rapunzel’s life has never gone as planned.

Twenty winters ago, before the Great Famine, Zel’s parents were caught stealing the fabled sorcerer’s rapunzel, the magical lettuce that grows around the base of his tall tower in the wood. He released them under the condition that when their yet unborn babe reaches adulthood, she will stay with him for one month before becoming his bride.
Then Zel was born a boy.
Only Zel’s parents know the truth, but while he was raised to pretend to be a girl, he will be no monster’s bride. He will use his month in the tower to unravel the mystery of the sorcerer’s immortality, so he might slay his would-be bridegroom and claim the tower and its treasures for the Thieves Guild.

What Zel does not know is that the sorcerer, Ulrich, has his own deceptions planned, and their journey of secrets, seduction, and identity might lead to revelations neither expect.